Urban Ecosystems, 3, 223–244, 1999
c 2000 Kluwer Academic Publishers. Manufactured in The Netherlands.
°
The natural South Florida system I: Climate,
geology, and hydrology
JAYANTHA OBEYSEKERA∗
South Florida Water Management District, Department of Research, West Palm Beach, FL 33406, USA
JOAN BROWDER
U.S. Department of Commerce, NOAA/National Marine Fisheries Service, Miami, FL 33149, USA
LEWIS HORNUNG
U.S. Army Corps of Engineers, Jacksonville District, Jacksonville, FL 32232-0019, USA
MARK A. HARWELL
Center for Marine and Environmental Analyses, Rosenstiel School of Marine and Atmospheric Science,
University of Miami, Miami, FL 33149, USA
Abstract. Developing hypotheses for sustainability requires an understanding of the natural forces that shaped
the historical Everglades prior to extensive engineering of the landscape. The historical Everglades marsh covered
10,000 km2 in a 100-km-long basin that has an extremely low gradient (slope of only 3 cm · km−1 ). The region
is characterized by a heterogeneous landscape that has developed over the past five millennia, functioning as an
interconnected mosaic of wetland, upland, estuarine, and marine ecosystems. The boundaries of this system were
defined as the historic drainage basin from the Kissimmee River system through Lake Okeechobee, the Everglades,
Florida Bay, and out through the Florida Keys to the coral reef tract. This geographic area is interconnected through
the regional hydrology, with its unifying surface and subsurface freshwater transport system. However, in the final
analysis, the interaction of geologic and climatic processes determine the system’s hydrology, a major determinant
of community and landscape structure and the point of connectivity between natural and human systems. This
review examines the role of climate, geology, soils and sediments, topography, and hydrology in shaping and
modifying ecological systems through time. However, it is clear from the wetland nature of this system that the
predrainage hydrologic features were critical to the sustainability of the Everglades. Important hydrologic features
include sufficient water quantity, storage, and sheetflow, and the appropriate hydroperiod and timing of water
releases over both annual and interannual variations in precipitation.
Keywords: predrainage Everglades, geologic and climatic process, regional hydrology, natural disturbances
Introduction
Developing hypotheses for sustainability requires an understanding of the natural forces that
shaped the historical Everglades prior to extensive engineering of the landscape. Ecosystems
are, in the final analysis, the end products of natural geologic and climatic factors (DeAngelis
and White, 1994). The interaction of geologic and climatic processes has and continues
to determine the system’s hydrology, which in South Florida is a major determinant of
community and landscape structure and is the point of connectivity between natural and
human systems.
∗ To
whom correspondence should be addressed.
224
OBEYSEKERA ET AL.
The driving forces that shape and modify ecological systems through time are of three
general types: (1) gradual and continuous changes (e.g., sea-level rise and climate changes);
(2) temporally discrete events or disturbances (e.g., fires, storms, floods); and (3) natural
periodicities (e.g., seasonal cycles of temperature and precipitation) (DeAngelis and White,
1994). Discrete (episodic) disturbances coupled with natural periodicities are the major
forcings shaping the South Florida ecosystem. The focus of this paper is to describe briefly
the historical climate, geology, and hydrology, and its relevance to defining the attributes
for a sustainable South Florida ecosystem.
Background
The South Florida ecosystem as defined encompasses an area of approximately 28,000 km2 ,
comprising nine major physical provinces dominated by the Kissimmee River system, Lake
Okeechobee, and Everglades watersheds (Interagency Science Subgroup Report, 1993). The
historical Everglades marsh covered 10,000 km2 in a 100-km-long basin with an extremely
low gradient (slope of only 3 cm · km−1 [Kushlan, 1989]). The region is characterized by a
heterogeneous landscape mosaic that has developed over the past five millennia (Interagency
Science Subgroup, 1993). This system functions as an interconnected mosaic of wetland,
upland, estuarine, and marine ecosystems. Ecosystem boundaries were defined as the historic drainage basin from the Kissimmee River system, from its headwaters in Kissimmee
Lake, through Lake Okeechobee, the Everglades, Florida Bay, and out through the Florida
Keys to the coral reef tract. The Immokalee Ridge and the Atlantic Coastal Ridge generally
marked the western and eastern boundaries of the Everglades. However, numerous flow
connections existed between the Everglades and the Atlantic Ocean, crossing the Atlantic
Coastal Ridge (also known as the Miami Ridge) through a series of channels called the
transverse glades. This geographic area was interconnected through the regional hydrology,
with its unifying surface and subsurface freshwater transport system. The physical system
itself, through the connectivity of water, whether natural or recently engineered, determines
the boundaries of an integrated ecosystem and consequently should define the boundaries
for ecosystem management.
The region of focus for the present case study is the South Florida human-dominated
ecosystem (figure 1). Within this region are some of the nation’s most diverse and intriguing ecological systems: the unique mosaic of the Everglades, the teeming nurseries of
subtropical estuaries, and the incredibly diverse coral reefs. The landscape and seascape
are dominated by an oligotrophic but highly productive surfacewater system. The fresh
water that flows in rivers, streams, and as a shallow sheet across the gently sloping landscape below Lake Okeechobee, through the tangled mangrove forests to the estuaries, and
out to the coral reef tract, is the unifying force and sustaining element of the system. The
US MAB International Biosphere Reserve (presently Everglades National Park), at the core
of the Greater Everglades ecosystem, is a treasured natural resource of significant value to
the region, nation, and world. Wading birds, alligators, sawgrass plains, mangroves, and
tropical hardwood hammocks are among its most recognizable features, but the essence
of the Everglades is the abundance and diversity of species that once lived among the
diverse range of habitats spanning vast open spaces (Douglas, 1947).
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
225
Figure 1. Key components of the South Florida regional system from the Kissimmee Lakes and river basin to
Lake Okeechobee, the Everglades, and Florida Bay.
226
OBEYSEKERA ET AL.
Prior to drainage and the initiation of large-scale water management, the entire system had
natural hydrological connections between its subsystems. The Everglades was an immense
wetland system south of Lake Okeechobee called the “river of grass” (Douglas, 1947) that
sprawled from the south shore of the Lake to the mangrove estuaries of Florida Bay and the
Gulf of Mexico. The Immokalee Ridge and the Atlantic Coastal Ridge generally marked
the western and eastern hydrologic boundaries of the Everglades, although numerous flow
connections across the coastal ridge overflowed water from the Everglades to the Atlantic
Ocean. The primary characteristics of the predrainage wetland ecosystem in the Everglades
were the hydrologic regime that featured slow sheetflow, a prolonged recession associated
with storage, large spatial scale, and heterogeneity in habitats.
Under natural conditions, the Lake had no direct outlet to the sea. The excess water
from rainfall and inflow exceeding evaporation spilled over the low southern shore into
the Everglades. This, along with rainfall, kept the Everglades flooded most of the year.
The southwestern corner of the Lake was particularly low, and that low area extended
southwestward to the headwaters of the Caloosahatchee River some 40 km from the actual
Lake Okeechobee shore. It was designated on early maps as the Great Okeechobee Marsh,
and it was undoubtedly the main outlet of overflow water from the Lake, if there could be
said to be a main outlet.
Today, within a few kilometers of this ecological paradise, more than 4.5 million people
live in urban centers growing at a rate of almost a million people per decade. Water, its
abundance once the critical characteristic of the natural system, has become the most limiting
resource. The lack of adequate quantities and timely distribution of clean water to coincide
with the system’s natural cycles has reduced the Everglades to a degraded remnant that is
continuing to decline. Only half of the natural Everglades remains in a near-natural state,
and a mere one-fifth of the original ecosystem falls within the boundaries of the US MAB
International Biosphere Reserve (Davis et al., 1994; Harwell and Long, 1995). As a result,
the Greater Everglades is an endangered ecosystem whose sustainability is critically at risk.
The defining physical and ecological characteristics of the natural Everglades are discussed here, to set the stage for subsequent discussions of the human alterations that have
developed over the past century. These defining characteristics have been well documented
in the scientific literature (Davis and Ogden, 1994; Harwell and Long, 1995; Interagency
Science Subgroup Report, 1993) and include large spatial scale; a hydrologic regime that
featured dynamic storage and sheetflow of highly oligotrophic water that traversed the landscape and entered Florida and Biscayne Bays; an expansive low-relief topography with a
shallow slope (3 cm · km−1 ); and heterogeneity in habitat with characteristic spatial and
temporal variation (Davis and Ogden, 1994; Interagency Science Subgroup Report, 1993;
Myers and Ewel, 1990).
The essence of the natural Everglades lies in the unique qualities and characteristics of
this ecosystem that humans so highly value, as defined by the ecological, hydrological, and
landscape factors that are essential for sustainability (Davis and Ogden, 1994).
Climate
The South Florida climate is characterized by the magnitude of spatial, annual, and intraannual variability. South Florida has a subtropical climate consisting of a 5-month wet season
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
227
that extends from late spring into the fall, and a dry season of roughly 7 months that extends
from late fall through spring. Superimposed on the main annual pattern are a short dry period
within the summer and, in some years, brief periods of heavy rains about midwinter. Two
phenomena are primarily responsible for the wet season rains: tropical storms, including
hurricanes, and thunderstorms related to convection. Winter rains are primarily associated
with the passage of cold fronts, which sweep down into South Florida in late winter, fall,
and early spring. Spring weather in South Florida is highly variable from year to year and
depends on the position and size of the Bermuda High, which can hamper convective cloud
development.
The Bermuda High is a semipermanent high-pressure system whose center is generally
located over the North Atlantic in the Bermuda-Azores area (Chen and Gerber, 1992).
During winter, the Bermuda High is generally small and is located to the south and east
of Florida. With the coming of spring, the pressure cell expands and migrates northward,
creating conditions in the air column that suppress convection. If the western extension
of the Bermuda High persists, wet season rains are delayed and drought conditions are
experienced. Because of the seasonality of rainfall, potential evapotranspiration exceeds
rainfall during part of the year. Annual potential evaporation exceeds annual rainfall at
some locations in some years.
South Florida’s latitude and location on the eastern shore of a large land mass would
suggest a subhumid or arid climate, but the region is significantly moderated by the moistureladen influence of the Gulf of Mexico, Caribbean Sea, and Atlantic Ocean (Chen and
Gerber, 1992). The temperature variation from summer to winter is much less in South
Florida than in almost any other place within the continental United States. Mean daily
temperatures range from about 17◦ C to about 25◦ C, and mean maximum daily temperatures
range from about 22◦ C to about 30◦ C (NOAA, 1985). Temperatures consistently exceed
27◦ C from March through November and frequently exceed 25◦ C throughout the winter
months. Consequently, seasons are primarily defined by the wet–dry cycle rather than by
temperature differences.
Thomas (1974) described the seasonal and spatial variation in South Florida rainfall.
Annual rainfall is higher on the coastal ridge than inland, and mainland rainfall is higher
than rainfall in the Florida Keys. Average annual rainfall varied from 152–165 cm along
the Atlantic coastal ridge to 114–127 cm around Lake Okeechobee and 88–114 cm in the
Florida Keys. In general, differences in wet-season and dry-season rainfall become more
pronounced with distance south through Florida (Chen and Gerber, 1992). The exception is
Key West, where there is little difference between wet season and dry season rainfall (Chen
and Gerber, 1992), possibly because convective rainfall is less important there.
Not only do annual rainfall volumes and seasonal patterns differ, but the interannual
pattern of wet years and dry years varies spatially also. Analysis of long-term records
indicates that the drought years in southwest Florida often do not correspond to drought
years in Miami (Duever et al., 1986).
Evapotranspiration is particularly important to the thunderstorm–rainfall process because
it is the primary mechanism by which water leaves the ecosystem. Because of the seasonality
of rainfall, potential evapotranspiration exceeds rainfall during part of the year, particularly
in the spring (figure 2). In undisturbed South Florida wetlands, it has been estimated to
export on the order of 70–90% of the rainfall entering these systems (Duever et al., 1994).
228
Figure 2.
OBEYSEKERA ET AL.
Climate patterns in South Florida. After Duever et al. (1994).
Peak potential evapotranspiration rates occur in the spring (with high temperatures but low
relative humidity), but actual evapotranspiration rates are highest in the summer wet season
when surface water is more available.
Precipitation is highly seasonal, with about 60% of the precipitation occurring during the
period of June through September and only 25% during November through April (figure 2).
Precipitation in May and October is variable across years, depending on when the wet and
dry seasons begin and end (Duever et al., 1994). Mean annual precipitation is about 120 cm
to 160 cm across the Everglades (lower amounts occur in the north).
Wet-season precipitation is dominated by convective processes (local thunderstorms),
leading to high spatial and temporal variability. These convective processes begin as the
semipermanent mid-Atlantic–Bermuda High pressure system moves northward in early
summer, and continue until before the winter solstice when the returning high pressure
system provides vertical stability to the atmosphere. Tropical low pressures, tropical storms,
and hurricanes, bringing moisture from the Atlantic and Caribbean, significantly affect the
total monthly precipitation. These systems occur primarily during the months of August
through October, leading to a bimodal distribution of precipitation within the wet season. Both the mid-Atlantic high-pressure system and the incidence of tropical storms are
significantly affected by El Niño events. Consequently, interannual variability in precipitation can be large (ranging from 86 cm to 224 cm during the 1951–1980 period) (NOAA,
1985), although no significant change in long-term total annual rainfall has occurred during
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
229
the past century, based on data from the Ft. Myers weather station for the period 1892–1980
(Duever et al., 1994).
Episodic events are very important to the South Florida environment. These include periods of drought, flooding, freezes, and tropical and winter storms. If the westward extension
of the mid-Atlantic high-pressure system persists into the summer, the dry season is prolonged and sometimes leads to one or several years of drought conditions (Chen and Gerber,
1992). Drought years lead to reduced surface water and lowered water tables, extensively
affecting the biological communities (discussed below). However, the large areal extent of
the historical interconnected surface hydrological system buffered the intensity of droughts
by carrying over water from previous wet periods through individual drought years. The
structure of the dynamic hydrological system historically led to a time lag in the onset of
drought conditions in the lower parts of the Everglades. Droughts result in an increased
incidence of fire, opening areas for burning that may have accumulated significant aboveground biomass since the previous fire event. The ecological implications of fire (especially
effects from changes in the intensity and/or frequency of fires) are discussed later. Similarly, flooding over large expanses of the natural system occurred periodically, especially
following major tropical storm events.
Tropical storms in South Florida occur at a frequency of approximately once per year
and hurricanes about once per decade. This is illustrated by the major hurricanes that have
affected areas south of Lake Okeechobee this century (1910, 1926, 1935, 1945, 1947,
1960 [Donna], 1965 [Betsy], and 1992 [Andrew]). These events can bring high sustained
winds, often with considerable precipitation and flooding, and they provide mechanisms for
destruction of habitat and dispersal of plants and animals. Major destruction to mangrove
forests and changes in topography of mangrove zone by three of these hurricanes have been
documented (Armentano et al., 1995; Craighead, 1971; Tebeau, 1973).
Finally, the incidence of freezing events can affect the South Florida regional environment,
in many instances limiting the distribution of plant and animal populations. The proximity
to water ameliorates the intensity and incidence rate of freezing events, resulting in a higher
rate of occurrence in interior areas of the region than in coastal areas. Similarly, the surface
freshwater depths at the time of a freeze episode can significantly affect biological effects
at the local level. There is a north–south gradient in the frequency of freezes, but there are
no records of freezes occurring in the Lower Florida Keys.
Geology
The geology of South Florida, reviewed, synthesized, and illustrated by Gleason and Stone
(1994), shows the surface distributions of the main geologic formations in South Florida
(figure 3). The South Florida geologic substrate conforms to a pseudo-atoll lagoon surrounded by fossil reefs. A relatively impermeable central limestone bedrock underlies the
Everglades. Geologic processes that formed the Everglades took place during the past five
million years. The oldest rocks, found on the western side and beneath the southern trough,
are part of the Tamiami Formation, a Pliocene deposit. A Pliocene reef tract may have produced the original topographic high along the east coast. This was later overlain by oolitic
limestone during the Pleistocene, forming the coastal ridge. At least five to seven periods
230
OBEYSEKERA ET AL.
Figure 3. The geology of South Florida shows the surface distributions of the main geologic formations. From
Gleason and Stone (1994), figure 7.2.
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
231
of marine submergence of the Everglades area have occurred since the Tamiami Formation
was deposited. The present floor of the Everglades was deposited primarily during the
last period of marine submergence, the Sangamon interglacial. Conditions that created the
Everglades were initiated when the coastal ridge, after 100,000 years of exposure as land,
created a seal that partially blocked drainage of fresh water from the interior depression to
the Atlantic.
The Floridan Plateau is a broad, flat platform that extends out to the 50-fathom line
(∼100 m). Its existence for long periods of geological time reflects that a very stable,
tectonically quiet foundation supports the Florida peninsula. The large-scale changes that
have occurred over the Floridan Plateau have primarily been driven by alterations in sea
level: when sea level rose, the exposed land portion of the Plateau correspondingly became
smaller, and when sea level was lower than present, the land extended out onto the Plateau.
The extent of this process can be seen in three shorelines that have occurred within the
Quaternary Era, ranging from the early Pleistocene interglacial Wicomico shoreline, when
sea level was about 30 m higher than present and the sea extended well above the present
Lake Okeechobee, through the Wisconsinan shoreline of about 20,000 years before the
present (YBP) (the most recent glacial period), where sea level was more than 100 m below
present (Gleason and Stone, 1994) and the land surface became as wide as the Plateau itself,
to the present-day shoreline. Webb (1990) stated that most of the two dozen glacial episodes
of the Pleistocene produced geographic results similar to those just described.
Since the middle to late Holocene (about 6500 YBP), there has been a continued rise
in sea level along the Gulf and SE Atlantic coasts of North America. In South Florida,
rates of sea-level rise exceeded 50 cm · century−1 from 7500 to 5500 YBP and were about
20 cm · century−1 from 5500 YBP until 3200 YBP, at which time rates reduced to about
4 cm · century−1 . Associated with these rates, the sea-level elevations compared to present
were −6.2 m at 5500 YBP and −1.0 at 3200 YBP (Wanless et al., 1994). This very slow
relative rise in sea level for the last few millennia has resulted in the natural distribution of
broad coastal wetlands and freshwater marshes of South Florida, and it allowed the shallow
marine sediments and organic coastlines to build up, so that the coastal mangrove swamps
actually progressed seaward even as sea levels rose. The resultant low-gradient coastal
swamp provided a natural barrier to marine water and allowed the freshwater habitats
of the Everglades to spread seaward. However, the rate of sea-level rise has increased
considerably during the past 60 years, to a current rate of about 30 to 40 cm · century−1 .
This rate may be increased further in response to global climate change, approaching a rate
of 60 cm · century−1 by the middle of the 21st century (Wanless et al., 1994).
The Miami Limestone Formation consists of an upper unit of spherical grains (oolites)
and a lower unit consisting of fossilized bryozoans. The Anastasia formation consists of
quartz sands resulting from maritime deposition. Both the Miami and Anastasia Formations
date from the Sangamon interglacial. The sands of the Anastasia Formation are an important
component of the coastal ridge north from the present-day northern Dade County. Marine
sands also form the topographic high known as Immokalee Rise in southwestern Florida,
which seems to have developed as a submarine shoal (White, 1970).
In the broad, shallow seas that occurred above the submerged portions of the Floridan
Plateau, the warm, subtropical climate resulted in very high rates of carbonate sediment
232
OBEYSEKERA ET AL.
formation from both inorganic processes (i.e., precipitation of calcium carbonate in solution in seawater) and biological processes (e.g., production of coral and algal reefs).
Hoffmeister (1974) referred to the South Florida coastal region as a vast limestone factory,
distributed into an array of smaller factories of different processes located in different locations and at different geologic times. Two primary processes of limestone formation are
particularly important to the natural South Florida ecosystem: inorganically produced limestone (e.g., the oolitic of the Miami formation) and biologically produced limestone (e.g.,
the bryozoan-precipitated limestone that underlies much of the historical Everglades). The
oolitic limestones were originally formed underwater as small unconsolidated carbonate
egg-shaped sand grains (ooids) deposited in layers in the shallow, low-energy waters. When
sea levels lowered, these formations were exposed to precipitation, and some of the lime
was dissolved and reprecipitated around the ooids as cement, binding them together into
hard rock. Over many cycles of sea-level change, this process gradually built up the rock
formation to the height of the current Miami ridge, which provides the eastern boundary
for the natural Everglades.
The oolitic limestone overlies these bryozoan rocks, forming the oolitic and bryozoan
facies that together form the Miami Formation, providing the bedrock of the southern half
of the Everglades and the adjacent coastal ridge (Hoffmeister, 1974). Seaward extensions of
the oolitic Miami limestone formation form the baserock floor of Florida Bay. The Upper
Florida Keys are the exposed part of a fossil coral reef, whereas the Lower Keys represent
higher relief portions of the Miami oolite.
The Ft. Thompson and Anastasia Formations occur at the northern half of the Everglades
and the Miami Limestone formation at the southern half (figure 3). The Anastasia Formation
to the north and Miami Formation to the east bound the eastern side. The northern Everglades
are bordered on the western side by the Caloosahatchee Formation. The southern Everglades
on the western side by higher elevations of the Tamiami Formation.
The Fort Thompson Formation, which underlies the Everglades to the north of the Miami
Formation up to Lake Okeechobee (figure 3), is believed to have resulted from freshwater
calcitic muds deposited in systems similar to the marl prairies and marshes of the present
lower Everglades (Gleason and Stone, 1994). Modern freshwater calcitic muds are found in
association with thick mats of blue-green algal periphyton that precipitate calcium carbonate
crystals in these South Florida waters rich with calcium and bicarbonate (Gleason and Stone,
1994; Browder et al., 1994). This process is indicative of an annual hydroperiod of the peatforming marshes and therefore insufficient to support peat-generating macrophytes. The
frequent seasonal drying enhances precipitation of calcium carbonate by increasing concentrations of dissolved calcium and bicarbonate, and facilitates the oxidation of organic
deposits, preventing peat buildup. The calcitic mud system also requires high light penetration of the water column to support the periphyton (i.e., shallow water and low organic
content). These conditions existed throughout large expanses of the freshwater ecosystems
of the region.
Since the distribution of the plant communities is largely controlled by the underlying
geology and the topography of a location, the surface sediments (peats and mucks) of the
Everglades system are distributed similarly to the geology (figure 4). The nature of these
inorganic and organic sediment formation processes and the quiescence of the underlying
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
233
Figure 4. Organic and marl soils of freshwater origin compose most of the surface deposits in the Everglades.
From Gleason and Stone (1994), figure 7.7.
234
OBEYSEKERA ET AL.
geology of the plateau have led to a topographic relief for the region that does not exceed 7 m
regionally (with the peak at the oolitic Miami coastal ridge). Indeed, topographic differences
of only a few cm can determine the habitat that exists at a particular location.
Soils and sediments
Organic sediments of South Florida developed during recent geologic periods; the oldest
dated freshwater peat from the Everglades was deposited about 5500 YBP at the southern
end of Lake Okeechobee, and other areas as far south as the middle Everglades have been
dated to about 4500 YBP. Initial rates of deposit were about 7 cm · century−1 , increasing to
16 cm · century−1 during the past 1200 years. By contrast, calcitic mud formation rates were
about 3 cm · century−1 initially (5000 YBP), decreasing to a rate of about 1.2 cm · century−1
during the past 1000 years (Gleason and Stone, 1994).
In South Florida, the type of soil found in a given locale is strongly influenced by the period
of inundation at that locale. This is a function not only of the rainfall seasonality but also of
topographic variation and substrate permeability, which together determine the hydroperiod.
The organic sediments in South Florida (i.e., the peats and mucks, which form the Histosols
order of soils) are formed by long-hydroperiod (exceeding nine months) wetland or littoral
macrophyte communities, in which the roots and rhizomes of macrophytes, along with some
aboveground biomass, are effectively preserved through the inhibition of biodegradation
(Gleason and Stone, 1994; Kushlan, 1989). The prolonged flooding maintains anaerobic
conditions, preventing oxidation of the organic matter (Kushlan, 1989). The considerable
moisture-holding ability of peats maintains those anaerobic conditions even during periods
of low-water levels. The nature of local weathering materials and location relevant to currentand wind-borne redistribution of sediments also influences the soil at a given site.
Organic and marl soils of freshwater origin make up most of the surface deposits in
the Everglades (figure 4). The organic soils, principally peats and mucks, underlie most
of the Everglades, covering 7682 km2 (4774 mi2 ). They were formed by the accumulation
of dead plant parts under conditions that retarded their complete decay. In South Florida,
formation of organic soils began on a large scale during the Holocene, about 5000 YBP,
and was supported by a seasonally flooded freshwater wetland dominated by graminoid
vegetation. The freshwater calcite muds known as marl soils were formed by the precipitation of calcium carbonate from the water column as a consequence of chemical conditions
created by the photosynthesis of microscopic algae. These algae (periphyton) grew on the
marsh floor and the submerged stems and leaves of marsh vegetation. Peat accumulation
occurred in areas exposed to prolonged submergence. Calcite muds, on the other hand, are
thought to have formed in areas that dried several months in most years. Calcium carbonate
concentrations greater than that of rainwater are required for calcite precipitation, so dissolution of a limestone substrate somewhere is a necessary prerequisite to calcite deposition
(Gleason and Spackman, 1974). Sand is the third soil type found in South Florida. Soils
with high proportions of sand occur on the coastal ridge north of Miami and in southwest
Florida.
Calcium carbonate sediments of marine origin form the floor of Florida Bay (Scholl,
1966). The calcareous sediments of Florida Bay are derived from several sources. Stockman
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
235
et al. (1967) demonstrated that the green macroalgae Penicillus is a major contributor of
fine aragonite mud to Florida Bay. According to Ginsburg (1956), mollusk shells are the
origin of about 76% of the sediments. Other sources of Florida Bay sediments are sponge
spicules, foraminifera, ostracods, and corals.
Organic soils
Peats in the Everglades system result from the interplay of many factors, including the
bedrock material and topography, the hydroperiod and water flow regime, the incidence of
droughts and fires, and the overlying vegetation. Distinctive peats and mucks are differentiated by the overlying plant communities (Davis, 1946; Jones, 1948); Everglades peat
primarily derives from sawgrass (Cladium jamaicense). The thickness of the peat layers
ranged up to 4 m in deeper parts of the Everglades basin, with deposits thickest near the
southern shore of Lake Okeechobee. This mass of peat precluded water flow, thereby bounding the lake, extending the hydroperiod, and increasing the stability of the peat formation
(Kushlan, 1989).
Four types of peats occur within the Everglades (Gleason and Stone, 1994): Okeechobee
muck, Okeelanta peaty muck, Loxahatchee peat, and Everglades peat. The Okeechobee
muck and Okeelanta peaty muck were created by the deposition of organic material originating in other places. They occurred in areas exposed to overwash from Lake Okeechobee.
Okeechobee mucks formed a 100-km-long, 4-m-thick ridge along the southern rim of Lake
Okeechobee. Okeelanta peaty mucks formed in what may have been an overwash area east
of the Lake. The topography of the bedrock appears to have dictated the distribution of
Loxahatchee and Everglades peats within the Everglades. Loxahatchee peats were formed
in depressions by a vegetation community dominated by white water lily. Everglades peats
were formed from sawgrass growing on the bedrock high. Everglades and Loxahatchee
peats are best represented. Everglades peats cover 4420 km2 , Loxahatchee peat covers
2950 km2 , and Okeechobee muck and Okeelanta peaty muck cover 130 km2 and 105 km2 ,
respectively.
Okeechobee muck and Okeelanta peaty muck have a higher mineral content than Everglades or Loxahatchee peat. Mineral contents of the original soils vary from 35% to 70%
for Okeechobee muck to about 10% for Everglades peat. The fine mineral component of
the muck soils probably washed in from Lake Okeechobee.
Peat deposits in the Everglades were originally at their maximum thickness of about
3 m at Lake Okeechobee and tapered off to less than 1 m in the southern Everglades. The
peat deposits bordering Lake Okeechobee formed the greater part of the southern rim of
the Lake and raised its elevation. Submerged peat deposits at the southern end of Lake
Okeechobee suggest that the Everglades marsh once extended northward into the present
Lake Okeechobee (Gleason and Stone, 1994).
Mangrove peats form the floor of the intertidal zone that borders mainland South Florida.
The most extensive areas of mangrove peat deposition are along the southwest coast beginning at Whitewater Bay just north of Cape Sable (Gleason and Stone, 1994). Mangrove
peats, as well as peats of sawgrass and other freshwater plant derivations, are part of the
sedimentary sequence underlying Florida Bay (Davies, 1980).
236
OBEYSEKERA ET AL.
Marl soils and calcium carbonate sediments
Surface deposits of freshwater, low-magnesium calcitic silt termed “calcitic muds” or calcite
by Gleason et al. (1974) cover large areas of South Florida. The most extensive surface
deposits are in the southeastern Everglades and Big Cypress. Calcitic mud is the oldest
postglacial wetland sediment dated from the Everglades. Calcite deposits underlie much
of the peat deposits in the northern Everglades and form part of the bottom sediments of
Lake Okeechobee. Dates of origin and relative positions of the peat and muck layers in
the Everglades suggest that marl formation preceded peat formation. Interbedding of peat
and marl layers has been observed by Gleason and Spackman (1974) and suggests that the
climate may have varied over the past 5000 years, alternating from conditions favoring peat
formation to those favoring calcite formation.
An environment for formation of limy sediments continues to exist in Florida Bay, attracting geologists interested in studying depositional environments of limestone (Scholl,
1966). The thickest deposits form the extensive network of banks that cordon the bay into
an intricate lacework of interconnected shallow basins, called lakes. The banks are narrow
in northeastern Florida Bay and much broader (2–5 km across) in the western and southwestern part of the bay. The limestone floor of the bay is nearly flat. Calcareous sediments
began accumulating in the bay about 4000 years ago when the last rise in sea level flooded
the Florida Bay area. Scholl (1966) stated that bank formation probably occurred in areas
where slack water was produced by converging currents. Another theory of bank and basin
formation is that the lakes in Florida Bay are “drowned marsh rills” converted to bay environments by sea-level rise. Examples of such formations are the embayments and lakes
along the northern boundary of the bay (e.g., Madeira, Little Madeira, and Joe Bays, and
Cuthbert, Long, and West Lakes). Low islands ringed or covered with mangrove trees are
scattered across Florida Bay, occurring on portions of the banks above mean high water.
Hurricanes and tropical storms deposited levees of sediment along the island perimeters.
These created interior ponds on some of the islands.
Sandy soils
Although the area where sand predominates is limited in South Florida, quartz sand is found
mixed with other soils, including peat and marl, throughout South Florida. It is mixed
with calcareous shell fragments and marl in shallow soils throughout the Big Cypress
(Duever et al., 1986). The thickness of sand deposits that form surface soils increases
northward, both in southwest Florida and along the east coast ridge. The quartz sand found
in South Florida probably is Appalachian weathering material that was transported by
coastal currents and deposited in present inland locations during marine transgressions.
Redistribution by local currents and winds probably is responsible for the mixing of this
material with other sediments. The sands that contribute to our present coastal beaches and
barrier islands probably came from reworked offshore deposits rather than from rivers that
are depositing their sandy sediment in bays and estuaries instead of on the open coast (Pilkey
and Field, 1972). Calcareous sands predominate in Florida Bay, making up more than 90% of
unconsolidated sediments (Scholl, 1966). Deposition of quartz sand ended at Cape Florida
on the east coast and at Cape Romano on the west coast (Johnson and Barbour, 1990).
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
237
Soil relationships
The two main soil types in the Everglades are both the product of past conditions and
major influences on present conditions. Climate, as reflected in hydrology, as well as local
topography and substrate, determined the type of soil that would form at a given site.
Shorter hydroperiods favored calcite deposition, whereas longer hydroperiods allowed the
accumulation of organic soils. Characteristics of the soil helped determine the conditions
for plant growth. Presumably rapid growth rates led to a higher rate of peat accretion.
The surface of peat determined water levels not only in Lake Okeechobee but also in
the Everglades. Each incremental increase in peat depth raised the head of freshwater that
balanced against saltwater and determined the location of the salt front in the permeable
limestone layers of the coastal ridge bordering the Everglades on the east. The natural peat
deposits made the water table in the Everglades and the coastal ridge relatively independent
of sea levels. Freshwater peat deposition in the central Everglades (areas of the present
Water Conservation Areas) began when the sea level was below the land surfaces where
deposition was occurring (Gleason and Stone, 1994).
In freshwater wetlands, soils reflect the long-term hydrologic history of a site (Tropical
BioIndustries, 1990), particularly with respect to frequency and duration of drying. This
is usually expressed in terms of hydroperiod, the number of months each year in which
soils are saturated or under water. Peats are indicative of longer hydroperiod sites, whereas
marls indicate shorter hydroperiod sites. Loxahatchee peats appear to have formed in areas
that were continuously submerged, whereas Everglades peats formed in areas that dried
seasonally, although not long enough to promote the formation of calcite. Calcite, or marl
soils, formed in areas that dried several months in most years.
The pattern of distribution of Loxahatchee peats suggests that there were at least two major
sloughs through the Everglades prior to drainage. One was in the area now known as the
Loxahatchee Wildlife Refuge (Water Conservation Area 3A). The other, larger area formed
a broad, elongated, slightly northwest-to-southeast-oriented strip inside the western rim of
the Everglades, starting just above what is now the Broward County line and narrowing and
sweeping southwestward, forming Shark Slough, the major watercourse through what is
now Everglades National Park.
The slough areas delineated by the occurrence of Loxahatchee peats conform to areas of
low relative elevations in the underlying Everglades bedrock named by Gleason and Stone
(1994). For instance, the area of Loxahatchee peats coincides with the southern part of
the bedrock low dubbed the Loxahatchee Channel. Loxahatchee peats in the west central
Everglades correspond in area to the Tamiami Basin. Those in the southern Everglades
correspond in location to the Shark River Bedrock Slough.
Their elevation relative to adjacent areas may explain why the areas of Loxahatchee
peat were wet continuously. Low areas not only can absorb and hold more water but also
receive inflows of freshwater from areas that are higher than they are. Groundwater seepage
can be particularly important because it is prolonged into the dry season. The eastern area
of Loxahatchee peats is downstream from Lake Okeechobee and connected to it by the
upper portion of the Loxahatchee Channel. The upper portion of the Loxahatchee Channel
coincides with Okeelanta peaty muck, a sediment with a high component of mineral material
received as overwash from Lake Okeechobee. Its occurrence, as well as the bedrock channel,
238
OBEYSEKERA ET AL.
suggests flow of water from Lake Okeechobee to the lower Loxahatchee Channel area
through this route. Additionally, the eastern area of Loxahatchee peat is located immediately
west of the thick Andalusian sand deposits that form the northern part of the coastal ridge.
Perennially wet conditions in the eastern, Hillsboro Lake, portion of the Loxahatchee area
may have been sustained by groundwater seeping from the western side of the sandy ridge.
Sandy aquifers release water more gradually than limestone aquifers, and therefore seepage
from a sandy aquifer would be expected to be more sustained through the dry season.
By analogy, a major source of the continuous flow of water to the strip of Loxahatchee
peats in the western central Everglades may have been the sandy flatlands of what is now
western Hendry County. These rise eventually to an elevation of 8.5 m on Immokalee Rise,
a thick sand deposit that contains the highest mainland point in southwest Florida.
Both the eastern and western Loxahatchee peat areas probably also received gradual
surface runoff and seepage water from adjacent higher areas of Everglades peat. In order
for perennially wet conditions to have been maintained, the upper western slough must
have received seepage water from higher surrounding areas and fed it to Shark Slough
on a consistent basis, even during dry periods. While high water flows were undoubtedly
carried into Shark Slough by the entire Everglades expanse defined by both Loxahatchee
and Everglades (sawgrass) peats, groundwater seepage from adjacent higher areas may have
been a source area for water to Shark Slough that was volumetrically important during times
of low rainfall. Shark Slough also was likely fed during the wet season and early dry season
by seepage from the lower east coast ridge on the east and the Big Cypress on the west.
Alternating layers of Loxahatchee and Everglades peats as well as alternating layers of
Everglades peat and calcite suggest that long-term variations in the hydrologic regime have
occurred in the past and have affected the type of soil formed at a given site. Charcoal fragments in sawgrass peats indicate the pervasiveness of fire in the prehistoric Everglades, but no
widely correlated charcoal layer has been found that would suggest periods of region-wide
fires. Therefore the estimated long-term average rate of peat formation (8.4 cm · century−2 )
is fairly accurate.
Radiocarbon dating suggests that peat profile development began slowly and then accelerated (Gleason and Stone, 1994). This may be because the peat, by retaining water, improved
conditions for vegetation growth and the subsequent preservation of organic matter. The fact
that an increasing rate of peat accumulation occurred concurrently with a decreasing period
of sea-level rise indicates that peat formation, once initiated, can be relatively independent
of sea-level rise. The relatively low permeability of the limerock underlying the Everglades
may have promoted peat formation; Gleason et al. (1974) suggested that the more porous
bedrock surfaces such as those found along the eastern edge of the Everglades may have
delayed the ponding of water and onset of peat deposition.
Topography
The relatively low topographic relief and variation of South Florida are defining physical
characteristics and merit special discussion. In the predrainage system, and to some extent
today, topographic variation controlled surfacewater flow, water retention, and groundwater
seepage. Three topographic scales were of major significance. The largest scale relates to
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
239
the general downward elevation trend from Lake Okeechobee (6.22 m) to the southwestern
coast with a gradient of approximately 6.82 cm · km−1 (Harshberger, 1914). A similar
topographic scale is the natural dividing line between the slopes of the Everglades toward
the Gulf of Mexico and toward the Atlantic Ocean. An intermediate spatial scale concerns
elevation differences between physiographic regions (e.g., the Everglades and the Atlantic
coastal ridge). The third and smallest scale is the local topography, which includes features
such as tree islands and ponds within the marshes and wet prairies.
The regional topography of mainland South Florida is best defined by White’s (1970)
seven physiographic regions. The regional highs are the Atlantic coastal ridge and Immokalee Rise. The Big Cypress spur is next to them in elevation. Slightly lower are the eastern
(St. Lucie area) and Caloosahatchee valleys. The Everglades forms the large swale between
the higher formations. The southern and southwestern coastal slopes and the coastal swamps
trend downward to the Atlantic coast and estuaries, Florida Bay, and the Gulf of Mexico.
Inland, local topographic variation was determined by differences in rates of weathering
of limerock substrate, local consumption of organic substrates by dry-season fires, the
earth-moving activities of alligators, and battery formation. The latter is a process in which
submerged, oxygen-rich polygons of peat break off from the bottom, rise to the water
surface, and lodge against emergent vegetation, forming a spot of higher ground. The native
human inhabitants of the area prior to occupation by colonial settlers also contributed
higher ground with their discarded mollusk shells. Coastward, sediments deposited by
hurricanes, possibly augmented by peat accumulation, formed low ridges that ponded water
and defined vegetation patterns. Bedrock topography influenced the bottom topography
of Florida Bay, and this influenced the surface topography of the southern Everglades.
Many of the mudbanks and islands of Florida Bay overlie or are on the flanks of bedrock
depressions (Wanless and Tagett, 1989). The locations and configurations of others were
influenced by sediment depositions along now-flooded former shorelines. Some of the
relationships to bedrock have been obscured by bank migration. The locations of the major
sloughs within the Everglades conform to the locations of major bedrock depressions. Both
limestone outcroppings and bedrock depressions over which peat deposits have accumulated
are represented by higher elevation sites in the southern Everglades.
Hydrology
The interplay of the geology, topography, and climatology defines the hydrology of the
South Florida regional environment. Historically, the Everglades began at Lake Okeechobee, which received its surface water inputs from the Kissimmee River basin to the
north. Outflows from the lake into the Everglades occurred intermittently during periods
of high water levels (Kushlan, 1989), but the influence of the input from Lake Okeechobee
diminished along a transect extending south through the Everglades. There the precipitation
within the Everglades itself was the dominant source of surface freshwater.
Dynamic water storage and sheetflow resulted from the very shallow elevation gradient,
the extensive areas of emergent wetland macrophyte vegetation, the thick peat and muck
substrates, and the highly permeable limestone bedrock (Fennema et al., 1994). Historically, large water masses constantly moved downslope (to the south and southwest), but
240
Figure 5.
OBEYSEKERA ET AL.
Hydroperiod comparison for natural and managed systems; mean annual (1965–1990) values.
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
241
at such slow rates that water was effectively banked from one wet season through the dry
season to the next wet season; transport times varied from months to years. Throughout
this system, groundwater seepage provided all of the base flow to creeks and rivers. The
interconnection of this surface flow hydrology with the groundwater system resulted in extended hydroperiods that related more to the large dynamic storage capacity of the system
and the delayed flow-through of the previous wet season’s precipitation than on the local
rainfall (figure 5). Consequently, wetlands were maintained in flooded conditions and with
continuous freshwater inflows well into the dry season. This carryover effect could maintain
surface waters in the wetlands, thus reducing the risk to the wetland ecosystems in drought
years, while maintaining continuous freshwater influxes into the estuaries even across one
or more drought years (Fennema et al., 1994).
Hydrologic models
Defining and understanding historic hydrology and its relationship to ecological patterns is
fundamental to the restoration process. A basic assumption is that hydrologic restoration,
in most of its facets, will lead to the recovery of the South Florida ecosystem. Ideally, a test
of this hypothesis will require a new generation of ecological models that will be coupled to
natural systems hydrologic models. The availability of natural systems hydrology models,
which are corollaries of present system hydrological models that have been calibrated using
present data, provides the basis for exploring a wide range of management scenarios. The
examination of restoration options will be guided by natural systems hydrologic models
coupled with a series of spatially explicit simulation models of species or guilds at the
landscape level.
Conclusions
Ecosystems are ultimately the products of exogenous forces of climate and geology, including insolation, temperature, precipitation, overland and groundwater flow, storm intensity
and frequency, and nutrient input through weathering and precipitation (DeAngelis and
White, 1994). These driving forces govern the rates of a variety of processes, both biological
and physical, that directly build, destroy, or change biological structures of an ecosystem.
This is particularly true in the Everglades and South Florida where alterations in topography
and hydrology are the most important driving forces shaping the ecosystems.
The driving forces that characterize and define the predrainage Everglades included the
great expanse of wetlands characterized by the topographic features of low relief and gentle
slope (3 cm · km−1 ) that supported the unique hydrological features of this system. The
predrainage hydrologic features of critical importance to the sustainability of the Everglades
include sufficient water quantity, storage, and sheetflow, and the appropriate hydroperiod
and timing of water release during both annual and interannual variations of precipitation. In
addition, the topography and hydrology provided for extensive freshwater flows to Florida
Bay, creating an annual periodicity of alternating low and slightly hypersaline waters, which
were responsible for maintaining large areas of seagrasses and associated productivity and
communities.
242
OBEYSEKERA ET AL.
Acknowledgments
This article is contribution number US MAB HDS 052 of the U.S. Man and the Biosphere
(US MAB) Human-Dominated Systems Directorate (HDS) Series.
Funding for this study was provided, in part, by the US MAB Program (Grant #1753100110). US MAB is administered by the U.S. Department of State as a multiagency,
collaborative, interdisciplinary research activity to advance the scientific understanding of
human/environment interactions. Additional funding was received from the U.S. Army
Corps of Engineers, Waterways Experiment Station, Vicksburg, MS (Contract #DACW
39-94-K-0032) and the U.S. Department of Commerce/National Oceanic and Atmospheric
Administration (NOAA) through a UM/NOAA joint research project funded by the NOAA
Coastal Ocean Program as part of the University of Miami-NOAA Cooperative Institute for
Marine and Atmospheric Studies (CIMAS NA67RJ0149: Task 3 Coastal Ocean Ecosystems
Processes). This article does not necessarily represent the policies of US MAB, the U.S.
Department of State, any member agency of US MAB, the U.S. Army Corps of Engineers,
or the U.S. Department of Commerce/NOAA.
We would also like to acknowledge the support of the South Florida Water Management
District (SFWMD), and in particular, Cal Neidrauer and Randy Van Zee of the Hydrologic
Systems Modeling Division.
References
Armentano, T., Doran, R.F., Platt, W.J. and Mullins, T. (1995) Effects of Hurricane Andrew on coastal and interior
forests of southern Florida: overview and synthesis. Journal of Coastal Research 21, 111–144.
Browder, J. and Ogden, J.C. (1999) The natural South Florida System II: Pre-drainage ecology. Urban Ecosystems
3, 245–277.
Browder, J.A., Gleason, P.J. and Swift, D.R. (1994) Periphyton in the Everglades: spatial variation, environmental
correlates, and ecological implications. In Everglades: The Ecosystem and Its Restoration (S.M. Davis and J.C.
Ogden, eds.), pp. 379–418. St. Lucie Press, Delray Beach, FL.
Chen, E. and Gerber, J.F. (1992) Climate. In Ecosystems of Florida (R.L. Myers and J.J. Ewel, eds.), pp. 11–34.
University of Central Florida Press, Orlando, FL.
Craighead, F.C., Sr. (1971) The Trees of South Florida. Vol. I. The Natural Environments and Their Succession.
University of Miami Press, Coral Gables, FL.
Davies, T.D. (1980) Peat Formation in Florida Bay and Its Significance in Interpreting the Recent Vegetational
and Geological History of the Bay Area. Pennsylvania State University, University Park, PA.
Davis, J.H., Jr. (1946) The peat deposits of Florida: their occurrences, development, and uses. State of Florida
Department of Conservation. Florida Geological Survey Bulletin, No. 30.
Davis, S.M., Gunderson, L.H., Park, W.A., Richardson, J.R. and Mattson, J.E. (1994) Landscape dimension, composition, and function in a changing Everglades ecosystem. In Everglades: The Ecosystem and Its Restoration
(S.M. Davis and J.C. Ogden, eds.), pp. 419–445. St. Lucie Press, Delray Beach, FL.
Davis, S.M. and Ogden, J.C., eds. (1994) Everglades: The Ecosystem and Its Restoration. St. Lucie Press, Delray
Beach, FL.
DeAngelis, D.L. and White, P.S. (1994) Ecosystems as products of spatially and temporally varying driving
forces, ecological processes, and landscapes: a theoretical perspective. In Everglades: The Ecosystem and Its
Restoration (S.M. Davis and J.C. Ogden, eds.), pp. 9–27. St. Lucie Press, Delray Beach, FL.
Douglas, M.S. (1947) The Everglades: River of Grass. Rev. ed., 1988. Pineapple Press, Sarasota, FL.
Duever, M.J., Carlson, J.E., Meeder, J.F., Duever, L.C., Gunderson, L.H., Riopelle, L.A., Alexander, T.R., Myers,
R.L. and Spangler, D.P. (1986) The Big Cypress Preserve. National Audubon Society, New York, NY.
NATURAL CLIMATE, GEOLOGY, AND HYDROLOGY
243
Duever, M.J., Meeder, J.F., Meeder, L.C. and McCollom, J.M. (1994) The climate of South Florida and its role
in shaping the Everglades ecosystem. In Everglades: The Ecosystem and Its Restoration (S.M. Davis and J.C.
Ogden, eds.), pp. 225–248. St. Lucie Press, Delray Beach, FL.
Fennema, R.J., Neidrauer, C.J., Johnson, R.A., MacVicar, T.K. and Perkins, W.A. (1994) A computer model to
simulate natural Everglades hydrology. In Everglades: The Ecosystem and Its Restoration (S.M. Davis and J.C.
Ogden, eds.), pp. 249–289. St. Lucie Press, Delray Beach, FL.
Ginsburg, R.N. (1956) Environmental relationships of grain size and constituent particles in some South
Florida carbonate sediments. Bulletin of the American Association of Petroleum Geologists 40, 2384–
2427.
Gleason, P.J., Cohen, A.D., Smith, W.G., Brooks, H.K., Stone, P.A., Goodrich, R.L. and Spackman, W. (1974) The
environmental significance of Holocene sediments from the Everglades and saline tidal plain. In Environments
of South Florida: Present and Past (P.J. Gleason, ed.), pp. 287–341. Miami Geological Society Memoir 2,
Miami, FL.
Gleason, P.J. and Spackman, W., Jr. (1974) Calcareous periphyton and water chemistry in the Everglades. In
Environments of South Florida: Present and Past (P.J. Gleason, ed.), pp. 146–181. Miami Geological Society
Memoir 2, Miami, FL.
Gleason, P.J. and Stone, P. (1994) Age, origin and landscape evolution of the Everglades peatland. In Everglades:
The Ecosystem and Its Restoration (S.M. Davis and J.C. Ogden, eds.), pp. 149–197. St. Lucie Press, Delray
Beach, FL.
Harshberger, J.W. (1914) The Vegetation of South Florida, South of 27 300 North, Exclusive of the Florida Keys.
Transactions of the Wagner Free Institute of Science, Philadelphia, PA.
Harwell, M.A. and Long, J.F. (l995) US MAB Human Dominated Systems Directorate Report on Ecological and
Societal Sustainability. U.S. Man and the Biosphere Program, Washington, DC.
Hoffmeister, J.E. (1974) Land from the Sea. University of Miami Press, Coral Gables, FL.
Interagency Science Subgroup Report (1993) Federal Objectives for the South Florida Restoration. South Florida
Management and Coordination and Working Group, Interagency Science Subgroup, Miami, FL.
Johnson, A.F. and Barbour, M.G. (1990) Dunes and maritime forests. In Ecosystems of Florida (R.L. Myers and
J.J. Ewel, eds.), pp. 429–480. University of Central Florida Press, Orlando, FL.
Jones, L.A. (1948) Soils, Geology, and Water Control in the Everglades Region. University of Florida Agriculture
Experiment Station, Bulletin Number 442l. Gainesville, FL.
Kushlan, J.A. (1989) Wetlands and wildlife, the Everglades perspective. In Freshwater Wetlands and Wildlife (R.R.
Sharitz and J.W. Gibbons, eds.), pp. 773–790. CONF-8603101, DOE Symposium Series Number 61, Office of
Scientific and Technical Information, U.S. Department of Energy, Oak Ridge, TN.
Myers, R.L. and Ewel, J.J., eds. (1990) Ecosystems of Florida. University of Central Florida Press, Orlando, FL.
NOAA [National Oceanographic and Atmospheric Administration]. (1985) Climatography of the United States
No. 20, Climate Summaries for Selected Sites, 1951–1980, Florida. National Climatic Data Center, Asheville,
NC.
Pilkey, O.H. and Field, M.E. (1972) Onshore transportation of continental shelf sediment: Atlantic southeastern
United States. In Shelf Sediment Transport: Process and Pattern (D.J.P. Swift, D.B. Duane and O.H. Pilewy,
eds.), pp. 142–154. Dowden, Hutchinson, Ross, Stroudsburg, PA.
Scholl, D.W. (1966) Florida Bay: a modern site of limestone formation. In Encyclopedia of Oceanography (R.W.
Fairbridge, ed.), pp. 212–227. Chapman-Reinhold, New York, NY.
Stockman, K.W., Ginsburg, R.N. and Shinn, E.A. (1967) The production of lime mud by algae in South Florida.
Journal of Sedimentary Petrology 37, 633–648.
Tebeau, C.W. (1973) Past Environment from Historical Sources. South Florida Environmental Project, National
Park Service, U.S. Department of the Interior, Washington, DC.
Thomas, T.M. (1974) A detailed analysis of climatological and hydrological records of South Florida with reference
to man’s influence upon ecosystem evolution. In Environments of South Florida: Present and Past (P.J. Gleason,
ed.), pp. 82–122. Miami Geological Society Memoir 2, Miami, FL.
Tropical BioIndustries (1990) Hydroperiod Conditions of Key Environmental Indicators of Everglades National
Park and Adjacent East Everglades Area as Guide to Selection of an Optimum Water Plan for Everglades
National Park, Florida. Report to the U.S. Army Corps of Engineers, Jacksonville, FL (Contract Number
DACW 17-18-6-0031), by Tropical BioIndustries, Miami, FL.
244
OBEYSEKERA ET AL.
Wanless, H.R., Parkinson, R.W. and Tedesco, L.P. (1994) Sea level control on stability of Everglades wetlands.
In Everglades: The Ecosystem and Its Restoration (S.M. Davis and J.C. Ogden, eds.), pp. 199–223. St. Lucie
Press, Delray Beach, FL.
Wanless, H.R. and Tagett, M.G. (1989) Origin, growth and evolution of carbonate mudbanks in Florida Bay. Bull.
Mar. Sci. 44, 454–489.
Webb, S.D. (1990) Historical biogeography. In Ecosystems of Florida (R.L. Myers and J.J. Ewel, eds.), pp. 70–100.
University of Central Florida Press, Orlando, FL.
White, W.A. (1970) The Geomorphology of the Florida Peninsula. Geological Bulletin, No. 51. Bureau of Geology,
Florida Department of Natural Resources, Tallahassee, FL.